<!DOCTYPE html>
<html lang="zh" dir="ltr" class="client-nojs">
<head>
<title>结构体与联合体初始化</title>
<meta charset="UTF-8">
<meta name="generator" content="MediaWiki 1.21.2">
<link rel="shortcut icon" href="../../../common/favicon.ico">
<link rel="stylesheet" href="../../../common/ext.css">
<meta name="ResourceLoaderDynamicStyles" content="">
<link rel="stylesheet" href="../../../common/site_modules.css">
<style>a:lang(ar),a:lang(ckb),a:lang(fa),a:lang(kk-arab),a:lang(mzn),a:lang(ps),a:lang(ur){text-decoration:none}#toc{display:none}.editsection{display:none}
/* cache key: mwiki1-mwiki_zh_:resourceloader:filter:minify-css:7:15cea3ec788a65b5187d4018eed543bf */</style>

<script src="../../../common/startup_scripts.js"></script>
<script>if(window.mw){
mw.config.set({"wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"c/language/struct_initialization","wgTitle":"c/language/struct initialization","wgCurRevisionId":70976,"wgArticleId":7975,"wgIsArticle":true,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":["Todo with reason"],"wgBreakFrames":false,"wgPageContentLanguage":"zh","wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"zh","wgMonthNames":["","1月","2月","3月","4月","5月","6月","7月","8月","9月","10月","11月","12月"],"wgMonthNamesShort":["","1月","2月","3月","4月","5月","6月","7月","8月","9月","10月","11月","12月"],"wgRelevantPageName":"c/language/struct_initialization","wgUserVariant":"zh","wgRestrictionEdit":[],"wgRestrictionMove":[]});
}</script><script>if(window.mw){
mw.loader.implement("user.options",function(){mw.user.options.set({"ccmeonemails":0,"cols":80,"date":"default","diffonly":0,"disablemail":0,"disablesuggest":0,"editfont":"default","editondblclick":0,"editsection":0,"editsectiononrightclick":0,"enotifminoredits":0,"enotifrevealaddr":0,"enotifusertalkpages":1,"enotifwatchlistpages":0,"extendwatchlist":0,"externaldiff":0,"externaleditor":0,"fancysig":0,"forceeditsummary":0,"gender":"unknown","hideminor":0,"hidepatrolled":0,"imagesize":2,"justify":0,"math":1,"minordefault":0,"newpageshidepatrolled":0,"nocache":0,"noconvertlink":0,"norollbackdiff":0,"numberheadings":0,"previewonfirst":0,"previewontop":1,"quickbar":5,"rcdays":7,"rclimit":50,"rememberpassword":0,"rows":25,"searchlimit":20,"showhiddencats":0,"showjumplinks":1,"shownumberswatching":1,"showtoc":0,"showtoolbar":1,"skin":"cppreference2","stubthreshold":0,"thumbsize":2,"underline":2,"uselivepreview":0,"usenewrc":0,"watchcreations":0,"watchdefault":0,"watchdeletion":0,
"watchlistdays":3,"watchlisthideanons":0,"watchlisthidebots":0,"watchlisthideliu":0,"watchlisthideminor":0,"watchlisthideown":0,"watchlisthidepatrolled":0,"watchmoves":0,"wllimit":250,"variant":"zh","language":"zh","searchNs0":true,"searchNs1":false,"searchNs2":false,"searchNs3":false,"searchNs4":false,"searchNs5":false,"searchNs6":false,"searchNs7":false,"searchNs8":false,"searchNs9":false,"searchNs10":false,"searchNs11":false,"searchNs12":false,"searchNs13":false,"searchNs14":false,"searchNs15":false,"gadget-MathJax":1,"gadget-ColiruCompiler":1});;},{},{});mw.loader.implement("user.tokens",function(){mw.user.tokens.set({"editToken":"+\\","patrolToken":false,"watchToken":false});;},{},{});
/* cache key: mwiki1-mwiki_zh_:resourceloader:filter:minify-js:7:258d7cd6aa9aa67dee25e01fb6a9e505 */
}</script>
<script>if(window.mw){
mw.loader.load(["mediawiki.page.startup","mediawiki.legacy.wikibits","mediawiki.legacy.ajax"]);
}</script>
<style type="text/css">/*<![CDATA[*/
.source-c {line-height: normal;}
.source-c li, .source-c pre {
	line-height: normal; border: 0px none white;
}
/**
 * GeSHi Dynamically Generated Stylesheet
 * --------------------------------------
 * Dynamically generated stylesheet for c
 * CSS class: source-c, CSS id: 
 * GeSHi (C) 2004 - 2007 Nigel McNie, 2007 - 2008 Benny Baumann
 * (http://qbnz.com/highlighter/ and http://geshi.org/)
 * --------------------------------------
 */
.c.source-c .de1, .c.source-c .de2 {font: normal normal 1em/1.2em monospace; margin:0; padding:0; background:none; vertical-align:top;}
.c.source-c  {font-family:monospace;}
.c.source-c .imp {font-weight: bold; color: red;}
.c.source-c li, .c.source-c .li1 {font-weight: normal; vertical-align:top;}
.c.source-c .ln {width:1px;text-align:right;margin:0;padding:0 2px;vertical-align:top;}
.c.source-c .li2 {font-weight: bold; vertical-align:top;}
.c.source-c .kw1 {color: #0000dd;}
.c.source-c .kw2 {color: #0000ff;}
.c.source-c .kw3 {color: #0000dd;}
.c.source-c .kw4 {color: #0000ff;}
.c.source-c .co1 {color: #909090;}
.c.source-c .co2 {color: #339900;}
.c.source-c .coMULTI {color: #ff0000; font-style: italic;}
.c.source-c .es0 {color: #008000; font-weight: bold;}
.c.source-c .es1 {color: #008000; font-weight: bold;}
.c.source-c .es2 {color: #008000; font-weight: bold;}
.c.source-c .es3 {color: #008000; font-weight: bold;}
.c.source-c .es4 {color: #008000; font-weight: bold;}
.c.source-c .es5 {color: #008000; font-weight: bold;}
.c.source-c .br0 {color: #008000;}
.c.source-c .sy0 {color: #008000;}
.c.source-c .sy1 {color: #000080;}
.c.source-c .sy2 {color: #000040;}
.c.source-c .sy3 {color: #000040;}
.c.source-c .sy4 {color: #008080;}
.c.source-c .st0 {color: #008000;}
.c.source-c .nu0 {color: #000080;}
.c.source-c .nu6 {color:#000080;}
.c.source-c .nu8 {color:#000080;}
.c.source-c .nu12 {color:#000080;}
.c.source-c .nu16 {color:#000080;}
.c.source-c .nu17 {color:#000080;}
.c.source-c .nu18 {color:#000080;}
.c.source-c .nu19 {color:#000080;}
.c.source-c .ln-xtra, .c.source-c li.ln-xtra, .c.source-c div.ln-xtra {background-color: #ffc;}
.c.source-c span.xtra { display:block; }

/*]]>*/
</style><style type="text/css">/*<![CDATA[*/
.source-text {line-height: normal;}
.source-text li, .source-text pre {
	line-height: normal; border: 0px none white;
}
/**
 * GeSHi Dynamically Generated Stylesheet
 * --------------------------------------
 * Dynamically generated stylesheet for text
 * CSS class: source-text, CSS id: 
 * GeSHi (C) 2004 - 2007 Nigel McNie, 2007 - 2008 Benny Baumann
 * (http://qbnz.com/highlighter/ and http://geshi.org/)
 * --------------------------------------
 */
.text.source-text .de1, .text.source-text .de2 {font: normal normal 1em/1.2em monospace; margin:0; padding:0; background:none; vertical-align:top;}
.text.source-text  {font-family:monospace;}
.text.source-text .imp {font-weight: bold; color: red;}
.text.source-text li, .text.source-text .li1 {font-weight: normal; vertical-align:top;}
.text.source-text .ln {width:1px;text-align:right;margin:0;padding:0 2px;vertical-align:top;}
.text.source-text .li2 {font-weight: bold; vertical-align:top;}
.text.source-text .ln-xtra, .text.source-text li.ln-xtra, .text.source-text div.ln-xtra {background-color: #ffc;}
.text.source-text span.xtra { display:block; }

/*]]>*/
</style><!--[if lt IE 7]><style type="text/css">body{behavior:url("/mwiki/skins/cppreference2/csshover.min.htc")}</style><![endif]--></head>
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_language_struct_initialization skin-cppreference2 action-view cpp-navbar">
        <!-- header -->
        <!-- /header -->
        <!-- content -->
<div id="cpp-content-base">
            <div id="content">
                <a id="top"></a>
                <div id="mw-js-message" style="display:none;"></div>
                                <!-- firstHeading -->
<h1 id="firstHeading" class="firstHeading">结构体与联合体初始化</h1>
                <!-- /firstHeading -->
                <!-- bodyContent -->
                <div id="bodyContent">
                                        <!-- tagline -->
                    <div id="siteSub">来自cppreference.com</div>
                    <!-- /tagline -->
                                        <!-- subtitle -->
                    <div id="contentSub"><span class="subpages">&lt; <a href="../../c.html" title="c">c</a>‎ | <a href="../language.html" title="c/language">language</a></span></div>
                    <!-- /subtitle -->
                                                            <!-- bodycontent -->
                    <div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr"><div class="t-navbar" style=""><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../../c.html" title="c"> C</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em">
<tr class="t-nv"><td colspan="5"> <a href="../language.html" title="c/language">语言</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../header.html" title="c/header">头文件</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../types.html" title="c/types">类型支持</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../program.html" title="c/program">程序工具</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../variadic.html" title="c/variadic">变参数函数支持</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../memory.html" title="c/memory">动态内存管理</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../error.html" title="c/error">错误处理</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../chrono.html" title="c/chrono">日期和时间工具</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../string.html" title="c/string">字符串库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../algorithm.html" title="c/algorithm">算法</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../numeric.html" title="c/numeric">数值</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../io.html" title="c/io">输入/输出支持</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../locale.html" title="c/locale">本地化支持</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../thread.html" title="c/thread">线程支持</a> <span class="t-mark-rev t-since-c11">(C11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../atomic.html" title="c/atomic">原子操作</a> <span class="t-mark-rev t-since-c11">(C11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../experimental.html" title="c/experimental">技术规范</a> </td></tr>
</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../language.html" title="c/language">C 语言</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em">
<tr class="t-nv-h2"><td colspan="5"> <a href="basic_concepts.html" title="c/language/basic concepts">基本概念</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../keyword.html" title="c/keyword">关键词</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../preprocessor.html" title="c/preprocessor">预处理器</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="statements.html" title="c/language/statements">语句</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="expressions.html" title="c/language/expressions">表达式</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="initialization.html" title="c/language/initialization">初始化</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="declarations.html" title="c/language/declarations">声明</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="functions.html" title="c/language/functions">函数</a></td></tr>
<tr class="t-nv"><td colspan="5"> 杂项</td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="history.html" title="c/language/history">C 的历史</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../experimental.html" title="c/experimental">技术规范</a> </td></tr>
</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="initialization.html" title="c/language/initialization">初始化</a><div class="t-navbar-menu"><div><div style="display:inline-block">
<div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em">
<tr class="t-nv"><td colspan="5"> <a href="initialization.html#.E6.98.BE.E5.BC.8F.E5.88.9D.E5.A7.8B.E5.8C.96" title="c/language/initialization">显式初始化</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="initialization.html#.E9.9A.90.E5.BC.8F.E5.88.9D.E5.A7.8B.E5.8C.96" title="c/language/initialization">隐式初始化</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="initialization.html#.E9.9B.B6.E5.88.9D.E5.A7.8B.E5.8C.96" title="c/language/initialization">零初始化</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="scalar_initialization.html" title="c/language/scalar initialization">标量初始化</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="array_initialization.html" title="c/language/array initialization">数组初始化</a></td></tr>
<tr class="t-nv"><td colspan="5"> <strong class="selflink">结构体及联合体初始化</strong></td></tr>
</table></div>
</div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p><a href="initialization.html" title="c/language/initialization">初始化</a> <a href="struct.html" title="c/language/struct">struct</a> 或 <a href="union.html" title="c/language/union">union</a> 类型对象时，初始化器必须是成员初始化器的非空、花括号环绕、逗号分隔的列表：
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>=</b></code> <code><b>{</b></code> <span class="t-spar">表达式</span> <code><b>,</b></code> <code><b>...</b></code> <code><b>}</b></code>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>=</b></code> <code><b>{</b></code> <span class="t-spar">指派符</span> <span class="t-spar">表达式</span> <code><b>,</b></code> <code><b>...</b></code> <code><b>}</b></code>
</td>
<td> (2)
</td>
<td> <span class="t-mark-rev t-since-c99">(C99 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>其中 <span class="t-spar">指派符</span> 是一序列（空白符分隔或相邻的） <code><b>.</b></code> <span class="t-spar">成员</span> 形式的单独成员指派符，和 <code><b>[</b></code> <span class="t-spar">下标</span> <code><b>]</b></code> 形式的<a href="array_initialization.html" title="c/language/array initialization">数组指派符</a>。
</p><p><a href="initialization.html#.E9.9A.90.E5.BC.8F.E5.88.9D.E5.A7.8B.E5.8C.96" title="c/language/initialization">隐式地初始化</a>所有未显式初始化的成员均被<a href="initialization.html#.E9.9B.B6.E5.88.9D.E5.A7.8B.E5.8C.96" title="c/language/initialization">零初始化</a>。
</p>
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
<p>初始化 <a href="union.html" title="c/language/union">union</a> 时，初始化器列表必须只有一个成员，它初始化联合体的首个成员<span class="t-rev-inl t-since-c99"><span>，除非使用指派初始化器</span> <span><span class="t-mark-rev t-since-c99">(C99 起)</span></span></span>。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">union</span> <span class="br0">{</span> <span class="kw4">int</span> x<span class="sy4">;</span> <span class="kw4">char</span> c<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy4">;</span> <span class="br0">}</span>
  u <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span><span class="br0">}</span>,           <span class="co1">// 令 u.x 活跃，拥有值 1</span>
 u2 <span class="sy1">=</span> <span class="br0">{</span> .<span class="me1">c</span><span class="sy1">=</span><span class="br0">{</span><span class="st0">'<span class="es5">\1</span>'</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 令 u2.c 活跃，拥有值 {'\1','\0','\0','\0'}</span></pre></div></div>
<p>初始化 <a href="struct.html" title="c/language/struct">struct</a> 时，列表中的首个初始化器初始化首个被声明成员<span class="t-rev-inl t-since-c99"><span>（除非指定了指派符）</span> <span><span class="t-mark-rev t-since-c99">(C99 起)</span></span></span>，而所有后继的<span class="t-rev-inl t-since-c99"><span>无指派符</span> <span><span class="t-mark-rev t-since-c99">(C99 起)</span></span></span>初始化器，初始化先前表达式所初始化者之后的结构体成员。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> point <span class="br0">{</span><span class="kw4">double</span> x,y,z<span class="sy4">;</span><span class="br0">}</span> p <span class="sy1">=</span> <span class="br0">{</span><span class="nu16">1.2</span>, <span class="nu16">1.3</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// p.x=1.2, p.y=1.3, p.z=0.0</span>
div_t answer <span class="sy1">=</span> <span class="br0">{</span>.<span class="me1">quot</span> <span class="sy1">=</span> <span class="nu0">2</span>, .<span class="me1">rem</span> <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span> <span class="br0">}</span><span class="sy4">;</span>      <span class="co1">// div_t 中的成员顺序可以不同</span></pre></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>指派符导致后随的初始化器初始化该指派符所描述的结构体成员。然后初始化继续按声明顺序向前，从指派符所描述成员的下个成员开始。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> sec,min,hour,day,mon,year<span class="sy4">;</span><span class="br0">}</span> z
   <span class="sy1">=</span> <span class="br0">{</span>.<span class="me1">day</span><span class="sy1">=</span><span class="nu0">31</span>,<span class="nu0">12</span>,<span class="nu0">2014</span>,.<span class="me1">sec</span><span class="sy1">=</span><span class="nu0">30</span>,<span class="nu0">15</span>,<span class="nu0">17</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 初始化 z 为 {30,15,17,31,12,2014}</span></pre></div></div>
</td>
<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td></tr>
</table>
<p>提供多于成员的初始化器是错误。
</p>
<h3><span class="mw-headline" id=".E5.B5.8C.E5.A5.97.E5.88.9D.E5.A7.8B.E5.8C.96">嵌套初始化</span></h3>
<p>若结构体或联合体的成员是数组、结构体或联合体，则初始化器的花括号环绕列表中的对应初始化器，是对这些成员合法的任何初始化器，除了可以以下列方式省略其括号：
</p><p>若嵌套初始化器以左花括号开始，则直到其右花括号为止的整个嵌套初始化器，初始化对应的成员对象。每个左开花括号建立一个新的<i>当前对象</i>。当前对象的成员以其自然顺序初始化<span class="t-rev-inl t-since-c99"><span>，除非使用指派符</span> <span><span class="t-mark-rev t-since-c99">(C99 起)</span></span></span>：数组以下标顺序、结构体成员以声明顺序、仅初始化任何联合体的首个被声明成员。<a href="initialization.html#.E9.9B.B6.E5.88.9D.E5.A7.8B.E5.8C.96" title="c/language/initialization">零初始化</a>当前对象内未由闭花括号显式初始化的子对象。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> example <span class="br0">{</span>
    <span class="kw1">struct</span> addr_t <span class="br0">{</span>
       <a href="../types/integer.html"><span class="kw122">uint32_t</span></a> port<span class="sy4">;</span>
    <span class="br0">}</span> addr<span class="sy4">;</span>
    <span class="kw1">union</span> <span class="br0">{</span>
       <a href="../types/integer.html"><span class="kw120">uint8_t</span></a> a8<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy4">;</span>
       <a href="../types/integer.html"><span class="kw121">uint16_t</span></a> a16<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span>
    <span class="br0">}</span> in_u<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> example ex <span class="sy1">=</span> <span class="br0">{</span> <span class="co1">// struct example 的初始化器列表开始</span>
                     <span class="br0">{</span> <span class="co1">// ex.addr 的初始化器列表开始</span>
                        <span class="nu0">80</span> <span class="co1">// 初始化 struct addr_t 的唯一成员</span>
                     <span class="br0">}</span>, <span class="co1">// ex.addr 的初始化器列表结束</span>
                     <span class="br0">{</span> <span class="co1">// ex.in_u 的初始化器列表开始</span>
                        <span class="br0">{</span><span class="nu0">127</span>,<span class="nu0">0</span>,<span class="nu0">0</span>,<span class="nu0">1</span><span class="br0">}</span> <span class="co1">// 初始化 union in_u 的首个成员</span>
                     <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>若嵌套初始化器不以左花括号开始，则仅从列表采用足够的初始化器，以用于该成员数组、结构体或联合体的元素或成员；任何剩下的初始化器留待初始化下个结构体成员：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> example ex <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">80</span>, <span class="nu0">127</span>, <span class="nu0">0</span>, <span class="nu0">0</span>, <span class="nu0">1</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 80 初始化 ex.addr.port</span>
                                        <span class="co1">// 127 初始化 ex.in_u.a8[0]</span>
                                        <span class="co1">// 0 初始化 ex.in_u.a8[1]</span>
                                        <span class="co1">// 0 初始化 ex.in_u.a8[2]</span>
                                        <span class="co1">// 1 初始化 ex.in_u.a8[3]</span></pre></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>嵌套指派符时，成员的指派符后随外围结构体/联合体/数组的指派符。在任何嵌套的方括号初始化器列表中，最外层指派符指代<i>当前对象</i>，而且只在<i>当前对象</i>中选择要初始化的子对象。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> example ex2 <span class="sy1">=</span> <span class="br0">{</span> <span class="co1">// 当前对象为 ex2 ，指派符属于 struct example 的成员</span>
                       .<span class="me1">in_u</span>.<span class="me1">a8</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span><span class="sy1">=</span><span class="nu0">127</span>, <span class="nu0">0</span>, <span class="nu0">0</span>, <span class="nu0">1</span>, .<span class="me1">addr</span><span class="sy1">=</span><span class="nu0">80</span><span class="br0">}</span><span class="sy4">;</span> 
<span class="kw1">struct</span> example ex3 <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">80</span>, .<span class="me1">in_u</span><span class="sy1">=</span><span class="br0">{</span> <span class="co1">// 更改当前对象为联合体 ex.in_u</span>
                           <span class="nu0">127</span>,
                           .<span class="me1">a8</span><span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy1">=</span><span class="nu0">1</span> <span class="co1">// 此指派符指代 union in_u 的成员</span>
                      <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>若显式初始化任何子对象二次（在使用指派符时可能发生），则使用的初始化器，是较后出现于列表中的初始化器（可能不求值较早的初始化器）：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> n<span class="sy4">;</span><span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"a<span class="es1">\n</span>"</span><span class="br0">)</span>, <span class="co1">// 可能打印或跳过它</span>
                     .<span class="me1">n</span><span class="sy1">=</span><a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"b<span class="es1">\n</span>"</span><span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 始终打印</span></pre></div></div>
<p>尽管任何未初始化的子对象都被隐式初始化，若子对象的显式初始化在初始化器列表中出现较早，则同一子对象的隐式初始化决不会覆盖显式初始化（选择 clang 以观察正确的输出）：
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="kw1">typedef</span> <span class="kw1">struct</span> <span class="br0">{</span> <span class="kw4">int</span> k<span class="sy4">;</span> <span class="kw4">int</span> l<span class="sy4">;</span> <span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span> <span class="br0">}</span> T<span class="sy4">;</span>
<span class="kw1">typedef</span> <span class="kw1">struct</span> <span class="br0">{</span> <span class="kw4">int</span> i<span class="sy4">;</span>  T t<span class="sy4">;</span> <span class="br0">}</span> S<span class="sy4">;</span>
T x <span class="sy1">=</span> <span class="br0">{</span>.<span class="me1">l</span> <span class="sy1">=</span> <span class="nu0">43</span>, .<span class="me1">k</span> <span class="sy1">=</span> <span class="nu0">42</span>, .<span class="me1">a</span><span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">19</span>, .<span class="me1">a</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">18</span> <span class="br0">}</span><span class="sy4">;</span>
 <span class="co1">// 初始化 x 为 {42, 43, {18, 19} }</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    S l <span class="sy1">=</span> <span class="br0">{</span> <span class="nu0">1</span>,          <span class="co1">// 初始化 l.i 为 1</span>
           .<span class="me1">t</span> <span class="sy1">=</span> x,      <span class="co1">// 初始化 l.t 为 {42, 43, {18, 19} }</span>
           .<span class="me1">t</span>.<span class="me1">l</span> <span class="sy1">=</span> <span class="nu0">41</span>,   <span class="co1">// 更改 l.t 为 {42, 41, {18, 19} }</span>
           .<span class="me1">t</span>.<span class="me1">a</span><span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">17</span> <span class="co1">// 更改 l.t 为 {42, 41, {18, 17} }</span>
          <span class="br0">}</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"l.t.k is %d<span class="es1">\n</span>"</span>, l.<span class="me1">t</span>.<span class="me1">k</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// .t = x 显式设置 l.t.k 为 42</span>
                                    <span class="co1">// .t.l = 41 会隐式清零 l.t.k</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">l.t.k is 42</pre></div></div> 
</div>
<p>然而，当初始化器以左开花括号开始时，会完全重初始化其<i>当前对象</i>，并忽略其任何子对象的先前的显式初始化器：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> fred <span class="br0">{</span> <span class="kw4">char</span> s<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy4">;</span> <span class="kw4">int</span> n<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> fred x<span class="br0">[</span> <span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"abc"</span> <span class="br0">}</span>, <span class="nu0">1</span> <span class="br0">}</span>, <span class="co1">// 初始化 x[0] 为 { {'a','b','c','\0'}, 1 }</span>
                      <span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>.<span class="me1">s</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">'q'</span>   <span class="co1">// 更改 x[0] 为 { {'q','b','c','\0'}, 1 }</span>
                   <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> fred y<span class="br0">[</span> <span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"abc"</span> <span class="br0">}</span>, <span class="nu0">1</span> <span class="br0">}</span>, <span class="co1">// 初始化 y[0] 为 { {'a','b','c','\0'}, 1 }</span>
                     <span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="co1">// 当前对象现在是整个 y[0] 对象</span>
                             .<span class="me1">s</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">'q'</span> 
                            <span class="br0">}</span> <span class="co1">// 以 { {'q','\0','\0','\0'}, 0 } 替换 y[0]</span>
                    <span class="br0">}</span><span class="sy4">;</span></pre></div></div> 
</td>
<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td></tr>
</table>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
<p>初始化器列表可拥有尾随的逗号，它被忽略。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">double</span> x,y<span class="sy4">;</span><span class="br0">}</span> p <span class="sy1">=</span> <span class="br0">{</span><span class="nu16">1.0</span>,
                          <span class="nu16">2.0</span>, <span class="co1">// 尾随逗号 OK</span>
                          <span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<p>C 中，初始化器的花括号列表不能为空（注意 C++ 允许空列表，并且注意 C 中<a href="struct.html" title="c/language/struct">结构体</a>不能为空）：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> n<span class="sy4">;</span><span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">0</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// OK</span>
<span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> n<span class="sy4">;</span><span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 错误：初始化器列表不能为空</span>
<span class="kw1">struct</span> <span class="br0">{</span><span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 错误：结构体不能为空，初始化器列表不能为空</span></pre></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-until-c99"><td>
<p>在初始化任何存储期的聚合体时，初始化器列表中的每个表达式必须都是<a href="constant_expression.html" title="c/language/constant expression">常量表达式</a>。
</p>
</td>
<td><span class="t-mark-rev t-until-c99">(C99 前)</span></td></tr>
<tr class="t-rev t-since-c99"><td>
<p>同所有其他初始化，在初始化静态或<span class="t-rev-inl t-since-c11"><span>线程局域</span> <span><span class="t-mark-rev t-since-c11">(C11 起)</span></span></span><a href="storage_duration.html" title="c/language/storage duration">存储期</a>的聚合体时，初始化器列表中的每个表达式必须为<a href="constant_expression.html" title="c/language/constant expression">常量表达式</a>：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">static</span> <span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">char</span><span class="sy2">*</span> p<span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><a href="../memory/malloc.html"><span class="kw403">malloc</span></a><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 错误</span></pre></div></div>
<p>任何初始化器中的子表达式<a href="eval_order.html" title="c/language/eval order">求值顺序</a>为非确定顺序（但 C++11 起的 C++ 中不同）：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
<span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> x,y<span class="sy4">;</span><span class="br0">}</span> p <span class="sy1">=</span> <span class="br0">{</span>n<span class="sy2">++</span>, n<span class="sy2">++</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 未指定，但是良定义的行为：</span>
                                  <span class="co1">// n 以任意顺序自增二次</span>
                                  <span class="co1">// p 等于 {1,2} 和 {2,1} 都是合法的</span></pre></div></div>
</td>
<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td></tr>
</table>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr><td class="mbox-empty-cell"></td><td class="mbox-text" style="">本节未完成<br>原因：更多实用的示例，最好初始化某些接头结构体 </td></tr></table>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="co2">#include &lt;time.h&gt;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">char</span> buff<span class="br0">[</span><span class="nu0">70</span><span class="br0">]</span><span class="sy4">;</span>
    <span class="co1">// 指派初始化器简化成员顺序未指定的结构体的使用</span>
    <span class="kw1">struct</span> <a href="../chrono/tm.html"><span class="kw523">tm</span></a> my_time <span class="sy1">=</span> <span class="br0">{</span> .<span class="me1">tm_year</span><span class="sy1">=</span><span class="nu0">2012</span><span class="sy2">-</span><span class="nu0">1900</span>, .<span class="me1">tm_mon</span><span class="sy1">=</span><span class="nu0">9</span>, .<span class="me1">tm_mday</span><span class="sy1">=</span><span class="nu0">9</span>,
                          .<span class="me1">tm_hour</span><span class="sy1">=</span><span class="nu0">8</span>, .<span class="me1">tm_min</span><span class="sy1">=</span><span class="nu0">10</span>, .<span class="me1">tm_sec</span><span class="sy1">=</span><span class="nu0">20</span> <span class="br0">}</span><span class="sy4">;</span>
    <a href="../chrono/strftime.html"><span class="kw517">strftime</span></a><span class="br0">(</span>buff, <span class="kw4">sizeof</span> buff, <span class="st0">"%A %c"</span>, <span class="sy3">&amp;</span>my_time<span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/puts.html"><span class="kw836">puts</span></a><span class="br0">(</span>buff<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>可能的输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">Sunday Sun Oct  9 08:10:20 2012</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 标准（ISO/IEC 9899:2011）：
</li></ul>
<dl><dd><ul><li> 6.7.9/12-38 Initialization (p: 140-144)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 标准（ISO/IEC 9899:1999）：
</li></ul>
<dl><dd><ul><li> 6.7.8/12-38 Initialization (p: 126-130)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 标准（ISO/IEC 9899:1990）： 
</li></ul>
<dl><dd><ul><li> 3.5.7/9- Initialization 
</li></ul>
</dd></dl>
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

</table></div>
</div>

<!-- 
NewPP limit report
Preprocessor visited node count: 2000/1000000
Preprocessor generated node count: 8941/1000000
Post‐expand include size: 42963/2097152 bytes
Template argument size: 15739/2097152 bytes
Highest expansion depth: 17/40
Expensive parser function count: 0/100
-->

<!-- Saved in parser cache with key mwiki1-mwiki_zh_:pcache:idhash:7975-0!*!0!!zh!*!zh!* and timestamp 20211207194757 -->
</div>                    <!-- /bodycontent -->
                                        <!-- printfooter -->
                    <div class="printfooter">
                    来自“<a href="https://zh.cppreference.com/mwiki/index.php?title=c/language/struct_initialization&amp;oldid=70976">https://zh.cppreference.com/mwiki/index.php?title=c/language/struct_initialization&amp;oldid=70976</a>”                    </div>
                    <!-- /printfooter -->
                                                            <!-- catlinks -->
                    <!-- /catlinks -->
                                                            <div class="visualClear"></div>
                    <!-- debughtml -->
                                        <!-- /debughtml -->
                </div>
                <!-- /bodyContent -->
            </div>
        </div>
        <!-- /content -->
        <!-- footer -->
        <div id="cpp-footer-base" class="noprint">
            <div id="footer">
                        <div id="cpp-navigation">
            <h5>导航</h5>
            <ul><li><a href="https://zh.cppreference.com/w/c/language/struct_initialization">Online version</a></li><li>Offline version retrieved 2022-01-01 00:37.</li></ul></div>
                        <ul id="footer-info">
                                    <li id="footer-info-lastmod"> 本页面最后修改于2021年6月20日 (星期日) 09:54。</li>
                                    <li id="footer-info-viewcount">此页面已被浏览过11,367次。</li>
                            </ul>
                    </div>
        </div>
        <!-- /footer -->
        <script>if(window.mw){
mw.loader.state({"site":"loading","user":"missing","user.groups":"ready"});
}</script>
<script src="../../../common/skin_scripts.js"></script>
<script>if(window.mw){
mw.loader.load(["mediawiki.action.view.postEdit","mediawiki.user","mediawiki.page.ready","mediawiki.searchSuggest","mediawiki.hidpi","ext.gadget.MathJax","ext.gadget.ColiruCompiler"], null, true);
}</script>
<script src="../../../common/site_scripts.js"></script>
<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-2828341-1']);
_gaq.push(['_setDomainName', 'cppreference.com']);
_gaq.push(['_trackPageview']);
</script><!-- Served in 0.770 secs. -->
	</body>
<!-- Cached 20211207194757 -->
</html>